Laminated glass



20 posed to unite Aa sheet of cellulose acetate or celered that certain carbohydrate derivativesI such *20 .Patented Jan, 7, 193e i 2,026,987. 'I

UNIT-ED STATES PATENT orrfcs LAMINATED oLAss 'James G. McNally and Sterling S. Sweet, Roches- A ter, N. Y., assignors to Eastman Kodak Com,- lany, Rochester, N. Y., a corporation of Newv ork y e Application March 11, 1933, Serial' No. 660,406

8 Claims. (Cl. 49-81.5)

This invention relates to laminated or safety respect to sun-light and immune to photochemglass and to the process of producing it. More ical discoloration'or disintegration. Anotherobparticularly the invention relates to a new and ject is to provide a process for cementing preimproved process for the manufacture of this formed sheets of colloidized cellulose organic detype of glass wherein a relatively thin sheet of rivatives to glass surfaces. A specific object is to t transparent thermoplastic material, such as celprovide a new type 0T laminated-glass in Which lulose acetate, o r other cellulosic material, is incellulose acetate, 0r its equivalent, is Permanent--v terposed between and firmly secured tov sheets of ly and adhesively joined t0 glass by means 0f glass by means o'fa special adhesive or adhesion a special type 0f adhesive OI adhesiOn inducing inducing agent. substance. Other objects will hereinafter appear. 10v Heretofore many types of laminated glass have `We have carried on extensive research in the been made. In practically all of these products manufacture 0f safety glass' and have ccndllcted a sheet of transparent thermoplastic material is eXperiments using-a Wide variety 0f tllerrrlcplas-A interposed between the sheets of glass and adtlc materials fOr the interpcsed plastic layer and heslvely secured thereto by means of specialadmany different agents for eifecting adhesion. The l5 hesives or cements. In fact, the principal prob- Principal diilicultv enccuntered in making glass lems encountered in. the production @f1-,his Seof this character was to obtain a proper adhesive called safety glass have centered around the Se.. or adhesion 4inducing substance. After investilection of the proper adhesives. It has been progatinemany diierent compounds wehave discovlulose nitrate to glass by coating the cellulose ace; as the acid esters of cellulose derived from dicartate with various plasticizing substances such as bOXylic acids. Which esters contain at 'least One triacetin, interposing the treated plastic sheet 'befre'e carboxyl group are particularly effectivetween sheets of glass and applying heat and pres- Typical among these esters may be mentioned.; Sure, but notwithstanding the claims made for cellulose acetate phthalate, cellulose acetate acid 25 these methods, they have never' proved to be succinate. cellulose acetate diglycollate. and Wholly 'satisfactory and it has' been recognized. starch acetate succinate. The ester employed that a completely satisfactory product cannot be may be a Single acid ester 0f cellulcse-0r starch manufactured in this manuelor an ester containing a plurality of differing acyl 3o When using cellulose nitrate as the principal groups- It Will be noted, llOWeveI. that al1 0f 30 l plastic layer, itis found that the glass, even after these compounds have at least one acyl group relativelyshort periods of exposure, turns yellow having at least One free carlOOXyl glcup- Al' or even brown, due to photochemical decomposithough we do not conne ourselves to any partion of the cellulose'nitrate. It is, therefore, de-A ticular theory'or explanation of their, elfectivesirable to use a type of material which will withness in our process Yit appears that the presence 35 stand the action of. sun-light and is substantially of one or more free carboxyl groups therein gives unaffected by, PhOtOeheInical acti0n. Cellulose to these compounds their peculiar adhesive or acetate fully meets these requirements, but as adhesionfinducing properties and renders them above indicated, the prbleni has been t0 S0 semuch superior to any substances heretofore pro- 40 Cure the Cellulose acetate Sheet t0 the glaSS that` posed for the purpqse of laminating glass and it willdnot separate or chip off when injuredttbiy plastic mata-EL v a' sud en blow' It is of mst impotanc in Our process is' quite simple as far as its manip-A type of Safety glass that the adhesmn-w1u be of ulative details are concerned and'consists, in its l such a character that when the glass surface is esential features in mming I the surfaces of a broken, the broken particles of glass will remain t. l thin h t f th l ti te 1445 firmly stuck 4to the interposed plastic layer or rela wey s ee o ermop as c .ma na' e layers f such as cellulose acetate, forb example, with a so-v Our invention has as an object to overome lution of a mixed acid ester of cellulose 1n an Iappthe above mentioned prior'art dimculti'es and to Pmpria'te solvent inlrposmg me Sheet between y provide aproductin which glass sheets arerm? tWO Sheets 0f glass, and assemblmg andpressing 50 ly and, for all practical purposes, inseparably the composite sheet together under the influence united to an interposed layer of non-brittle ther- 0f lietY moplastic material. A further object is to pr- We will now describe our invention in detail vide a process for producing a tough,J strong, by reference to an example in which we have set transparent, laminated glass whlchis stable with 'forth one of the preferred embodiments of our 55 invention which is included merely for purposesN of illustration and not as a limitation.v

l Example 1 A Two sheets oiL glass approximately V4 inch thick are carefully cleaned, washed and dried.

A sheet of clear, transparent, cellulose acetate is tremely thin film consisting of a solution comsuch as benzyl alcohol is deposited on the surlface's of the plastic sheet. Optionally, a' surface of each of the glass sheets may be thus treated then placed in a platen press and pressed for three minutes at about 90 C. and a pressure of 100 lbs. per square inch to insure initial sticking together of the'various layers. The sheet isv then placed in a liquid pressure autoclave, such as is commonly used for this purpose in the glass making industry, and subjected to a uniform liquid pressure of 250 lbs. per square inch at a temperature of about 140 C. for about fteen minutes. After this heat and pressure treatment, the sheet N is cooled and washed, after which it is found that the glass is firmly and inseparably bound to the 35 interposed plastic material and that a strong,

clear, transparent' article is obtained.

Example 2 y Two sheets of glass are prepared as in Example 1 bythorough cleaning, washing, and drying. A illm isdeposlted on both surfaces of a sheet of clear, transparent cellulose acetate'plastic about .025 inch in thickness by spraying with a solu` tion prepared by dissolving 1 gram of cellulose acetate diglycollate in 10 grams of benzaldehyde. The sheet is then interposed between the glass plates and the'structure assembled and subjected for about ve minutes to 'a pressure of about 180 .pounds per square inch in a platen press at a temperature of 130 C.v The'sandwich is then removed from the platen press and subjected to a pressure of ,300 pounds per square inch in a liquid pressure autoclave at a temperature of 140 C. After removal from the. autoclave and 55 appropriate washing and drying, an lexcellent laminated glass structure is found to have been produced.

Example 3 A laminated glass structure is produced em- 60 ploying the same conditions of Example 2, except that the solution with which the cellulose 'acetate sheet is treated is formed by dissolving 1 gram of starch acetate succinate in 10 grams of benzyl s alcohol. As in the previous examples, an excel- 55 lent type of laminated glass results.

Referring to the drawing in which the structure of our new laminated glass product is more graphically shown and in which' it is understood that the relative thickness oi the respective 70 lamin are greatly-exaggerated for the sake of clearness, l

Fig. 1 is a sectional view illustrating the lamin Y before assembly; l

Fig. 2 is a secti nal view`il1ustrating the assembled glass sheet,

` face between the glass and'plastic thereof.

mined that practically all of `the essential adhel In Fig. 1, A and E designate sheets of' glass, the respective surfaces S and S' of which have been properly prepared by washing and drying.

C represents a thin sheet of cellulose acetate, treated on both surfaces with very thin lms B 5 and D of a. solution of cellulose acetate acid succinate dissolved in benzyl alcohol, and ready for assembling with the two glass sheets A and E.

In Fig. 2 is shown the composite sheet after assembling and pressing together in accordance 10 with the procedure outlined above. While we do not attempt to offerany theory as to the action of the adhesives or adhesion inducing materials used in our process, it seems probable that the mixed cellulose acid ester remains and produces some peculiar effect upon the plastic which causes it to adhere tenaciously to the glass, while vthe plasticizing solvent penetrates to a certain extent into the plastic and probably in some way 20 enhances the adhesive quality of the plastic surface in contact with the glass. Whatever the explanation, th'e resulting laminated glass sheets have a higher degree of adhesion to the interposed plastic material than has been heretofore attainable by employing any of the known types of adhesives or adhesion inducing substances. Our product will successfully withstand comparatively severe shocks and even direct blows of considerable force without shattering. If the material is subjected to blows of such force that the outer glass layers are broken,j the powerfulA adhesion between the glass and plastic prevents chipping ofl' or breaking away of the glass fragments. C We `wish again to call attention to the fact that Fig. 2 is merely aV graphic representation of the assembled laminated sheet and is not in` yten-ded as an exact showing of the actual structure, since under the influence of heat and pres-4 40 sure the extremely thin layers or lms B and D tend to merge with the plastic material of sheet C and as pointed out, thef plasticizing solvent probably tends to penetrate into the interior However, we have conclusively detersivefmaterial, i. e., the cellulose organic acid ester remains in the interface or area between' the glass and plastic. l

While we have described our invention by reference to the several typical compounds as the adhesive or adhesion inducing agents and by reference to a particular procedure, our invention is in n o way limited thereby. We may, for example, employ as such agents a wide variety of compounds of cellulose derived from dicarboxylic, v saturated yor unsaturated acidsy of both the aliphatic and aromatic series. We may employ any of the acid esters, such as the phthalates or succinates of cellulose, especially the esters prepared according to the methods outlined in the appli- ,cation of C. J. Malm and C. E. Waring, Serial No. 380,252 and containing a i'ree carboxyl group. This classification, therefore, includes cellulose -esters produced by the esteriilcation of one or 05 more of the esteriiiable` hydroxyl groups per CeH1nOs,'such as the mono, di-, or triphthalates, and the mono, di, and trisuccinates.

We may likewise employ cellulose esters having different acyl groups in the molecule, such as cellulose acetate acid phthalate, cellulose acetate diglycollate, cellulose acetate acid succinate, and even cellulose acetate tartrate. Other saturated acid groups may be present instead of acetyl, for example, formyl, propionyl, lactyl, and the like.

in the interl5 As explained above, it is apparently the presence ofA the free vcarboxyl groups in the ester which gives it its unexpected and distinguishing adhesive'properties, regardless of whether the ester is a single ester, that is-to say, one derived from a single acid, such asgsuccinic, phthalic, glycollic .and so on, or is a mixed ester containing different acyl groups. So long as the free carboxyl group is lpresent we Yhave f ound these esters to be eminently satisfactory for our purpose.

While we have described our invention with reference to cellulose derivatives, we are not limited thereto, as we may employ the single or mixed acid esters of monobasic and polybasic 'acids o f polymeric compounds containing free hydroxyl groups other than cellulose, such as those derivable from starch and inulin. Our invention is also applicable to the lamination of cellulose nitrate sheets 'to glass, as well as the lamination of a sheet of cellulose acetate overf coated with cellulose nitrate.

The cellulose acid esters above described may be dissolved in a variety of solvents, but we prefer to employ substances of low vapor pressure which areplasticizing solvents for the plastic material of the interposed sheet. Among these may be mentioned benzyl alcohol, benzyl acetate, triacetin, methyl "cellcsolve (the monomethyl ether of ethylene glycol), ethyl tartratefacetophenone,

:in ethyl acetanilid, salicylaldehyde, cinnamic acid,

hydroxy benzoyl alcohol, ethylene glycol monobenzyl ether and amyl borate. While we have described the use of a relatively dilute solution of the acid ester in the higher boiling solvent,

more concentrated solutions are satisfactory. On the other hand the concentration of the ester in i the solution may be much lower. In general, the amount of ester will be governed, not only by the degree of adhesion desired, but by the consistency of the resulting solution, it being obvious that highly concentrated solutions will be more viscous and therefore more diicult to apply to the plastic sheet.

We prefer to apply the adhesive solution to the plastic (or to the glass) by spraying as this method distributes the material in a more even lm than is possible'with any other, but. it may be applied by brushing, dipping or any equiva- -lent and convenient procedure. The details of the operations following the application of the adhesive may,r` also vary widely.

Although we prefer to subject the assembled sheets of glass and plastic to a comparatively moderate preliminary pressure, say in the vicinity of 100 lbs. per square inch and a temperature of about 90v C., we may vary this pressure and temperature, as likewise the nal pressure and temperature. In the second pressing operation a temperature of about140" C. is found satisfactorywith a pressure of Z50-450 lbs. It is apparent from the foregoing that a laminated glass comprising a single glass sheet laminated to a single plastic sheet may be produced or a plurality of layers of glass and plastic may be built up as in the manufacture of so-called bullet proof glass. In this latter type of glass lit is customary to interppse a comparatively thick sheet of glass between two thinner sheets,

- the latter being secured to the thicker sheets by means of interposed layers of thermoplastic material. In making this type 'of product the same diiiiculty has been experienced as in the manufacture o the ordinary product, namely, the difo cultycfobtaining the desired degree of adheu sion between ,the plastic material and the glass and, so far as we are aware this diiculty has never been entirely overcome until the, development of the present process.

It is further apparent that our invention has many advantages which commend it to the man- 5 ufacturer of laminated glass. It is comparatively simple as vfar as manipulative details are concerned, involves no substantial departure from established practice, and requires only the conventional types of apparatus used in the lami- 10 nated glass industry. It requires no pretreatment of the plastic sheet, such as the application of overcoatings of gelatin, cellulose nitrate or similar agents to produce the desiredtenacious adhesion between plastic and glass. l5

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as lde- 20 ned in the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. Laminated glass comprising glass and thermoplastic cellulose derivative sheets adhe- 25 sively bonded thereto by the agency of aiilm con- .taining a mixed carbohydrate organic ester at least one of the acyl groups oi which contains a free carboxyl group.

2. Laminated glass comprising a thermoplastic 30 sheet of cellulose derivative material bonded to sheets of glass and having between the cellulose derivative material and the glass a bonding .film comprising a mixed carbohydrate organic ester at least one of the acyl, groups of which con- 35 tains a free carboxyl group.

3. Laminated glass comprising a thermoplastic sheet of cellulose derivative material bonded to sheets of glass and having between the cellu- I lose derivative material and the glass a bonding 40 film comprising a mixed cellulose organic ester at least one of the acyl groups of which contains a free carboxyl group.

4. Laminated glass comprising a thermoplastic sheet of cellulose derivative material bonded to 45 sheets of glass and having between the vcellulose derivative material and the glass a bonding film comprising a mixed cellulose ester of a fatty acid, and a dicarboxylic acid, one of the acyl groups 'of which ester contains a free carboxyl group. 50

5. Laminated glass comprising` a thermoplastic sheet of cellulose derivative material bonded to sheets of glass and having between the cellulose derivative material .and the glass a bonding lm comprising a cellulose ester of acetic acid and a 55 dicarboxylic acid one of the acyl groups of which ester contains a free carboxyl group.

6. Laminated glass comprising a thermoplastic sheet of cellulose derivative material bonded to sheets of glass and having between the cellulose 60 derivative material and the glass a bending film comprising cellulose acetate succinate.

7. Laminated glass comprising a thermoplastic sheet of cellulose derivative material bonded to sheets of glass and having between the'cellulose 65 derivative material and the glass a bonding film comprisingv cellulose acetate phthalate.

8. Laminated glass comprising a thermoplastic sheet of cellulose derivative material bonded to sheets of glass and having between the cellulose 70 derivative material and the glass a bonding lm comprising cellulose acetate diglycollate.

JAMES G. McNArLY. STERLING s. SWEET. ,y 15 

